Since 1974, when a
study titled “Zinc ions inhibit replication of rhinoviruses” by Korant, Kauer,
and Butterworth was published in the journal Nature, the idea that zinc can
prevent or cure the common cold has circulated. Many studies have looked at
different zinc ionophores and lozenge formulas and their effect on the course
of cold symptoms, as well as the potential biochemical mechanism at work.
Though the exact mechanism of action is still unknown, there is some consensus
that ionized zinc affects picornaviruses.
Zinc Against Cold Viruses
Rhinoviruses, of the
family Picornaviridae, are only one type of almost 200 viruses that cause the
acute respiratory infection symptoms known as the
common cold. However, rhinoviruses are estimated to cause one-third to half
of all colds, and preventing rhinovirus
infections would severely limit the most common human infection.
Since the 1970s,
studies have found that zinc ions may inhibit rhinovirus replication. Viral
replication plays an important role in infection; inhibiting replication would
prevent progression of the disease and ease symptoms. In addition, zinc ions
have an affinity for the ICAM-1 receptor, which is bound by rhinovirus when
infecting cells in the respiratory tract. Zinc binding the ICAM-1, or the
rhinovirus-ICAM complex, would prevent infection of the nasal epithelium,
preventing the duration of the common cold.
What Type of Zinc Reduces Cold Symptoms?
In the 1980s and
1990s, zinc gluconate lozenges were shown in some studies to decrease the
duration of cold symptoms if taken within 24 hours of symptom onset, whereas
other studies had no success. Zinc acetate lozenges appeared to have a better
success rate, likely because of their formulation. The problem seems to lie in
the concentration of ionic zinc in commercially available lozenges. The ionic
zinc concentration is not measurable by the label on a package, it is dependent
on what is released as the lozenge dissolves in the mouth over a period of
time.
Zinc gluconate gels
and nasal sprays have had experimental success in alleviating rhinovirus
infection. Some formulations were even marketed, such as Zicam. However, these
products were recently warned against due to users losing their sense of smell.
Potential Problems with Zinc Products
Though zinc lozenges
have repeatedly been found to exert no side effects or create any problems,
beyond the chalky taste, zinc nasal sprays have been shown to irreversibly
damage the nasal lining. In particular, Zicam (zinc gluconate nasal spray from
Matrixx Initiatives) was shown in an October 2009 study to have cytotoxic
effects on both mouse and human olfactory sensory neurons, as well as a near
complete loss of the nasal epithelium and submucosa. Sprays not containing zinc
did not have this significant effect, indicating that the zinc was cytotoxic to
the nasal mucosa.
Using Zinc to Stop a Cold
Though it is far
from being a cure, there is evidence to suggest that zinc lozenges may help
reduce cold symptoms, cutting the duration of the illness in half and
alleviating symptoms more fully after the duration of the illness. A 2011 Cochrane Review concluded that zinc supplementation can reduce the duration and severity of a cold, though the change in duration is mostly by just 1 day. However, the
exact mechanism of action is not known, and the exact dosage will differ by
product. The guidance is to start with lozenges or tablets within 24 hours of the onset of a cold. In a 2017 meta-analysis, zinc acetate and zinc gluconate were shown to have similar effectiveness.
More studies are needed to better quantify
zinc’s effect on rhinovirus and other cold viruses in order to reap the full
benefit of this element.
Additional References:
Eby. Zinc lozenges
as cure for the common cold: A review and hypothesis. Medical Hypotheses. 2009; doi 10.1016/j.mehy.2009.10.017
Hulisz. Efficacy of
zinc against common cold viruses: An overview. Journal
of the American Pharmacists Association. 2004; 44(5). Available on the
Medscape website.
Lim et al. Zicam-induced
damage to mouse and human nasal tissue. Public
Library of Science (PLoS) One. 2009; 4(10), e7647.